I think you already seen official selenium documentation but it good place to start. Since you do not specified which Selenium tool you what to learn. For example Selenium IDE and Selenium with Web Driver is different tools and need different knowledge to use. While reading official documentation can help you to decide from which one begin learn.

It's a pay site, but it has been great for me. All video tutorials with optional online classes, great forums, access to interview q&a, covers java basics also. Also, has a lot of try before you buy videos you can check out to decide if you like it.